Abstract Because of significant treatment advances, over 80% of children diagnosed with cancer become long- term survivors; however, 70% develop chronic or life threatening late effects from treatment, and these often emerge during young adulthood. Detailed survivorship guidelines recommend annual long-term follow-up care (LTFU) to manage and monitor for late effects and recurrent or new cancer. As risk for late effects increases, engagement in cancer-related care plummets in young adulthood. Given adolescents and young adults (AYA) with a history of cancer are understudied and underserved, it is not surprising that reasons for the decline in LTFU across the transition to adulthood are elusive. Lack of transition readiness (indicators that patient can begin, continue, and finish the transition process through the transfer to adult-focused care) and self- management skills (ability to manage health conditions) may be aspects of self-management related to such decline. To elucidate risk factors for and patterns of AYA disengagement, we propose a prospective study of AYA survivorship self-management that focuses on transition readiness, self-management skills, and engagement in LTFU. This study represents an extension of Dr. Schwartz?s prior R21 (CA141332) developing and validating a social-ecological model of transition readiness (SMART) and companion measure (TRI). TRI extends extant measures of self- management and transition readiness, which mostly focus on skills, by also assessing broader social- ecological components of SMART (e.g., goals, relationships, beliefs). Initial validity and factor structure of the TRI item pool was established. Our current objectives are to: 1) finalize TRI via rigorous evaluation and calibration methods employed in the development of PROMIS measures, and 2) identify determinants and patterns of survivorship self-management--transition readiness, self-management skills, and engagement in LTFU--, and test the transactional relationship between these variables, by following an initial cohort of 600 diverse AYA survivors across 3 sites for 2 years. We hypothesize that indictors of self- management will be predicted by theoretically-informed and multi-factorial variables, and that engagement in LTFU will influence, and be influenced by, transition readiness and self-management skills over time. For those who are transferred to adult care, we will assess their experience at their last pediatric appointment and whether or not that related to uptake of adult-oriented care. Thus, we will continue our translational and multidisciplinary program of research by innovatively employing a prospective design and state-of-the-art methods to finalize TRI and test a model of AYA self-management related to engagement in LTFU. Results are critical for designing future interventions to enhance self- management of AYA, ultimately informing best practices for survivorship care to sustain engagement and well-being of AYA survivors. The study is consistent with NINR?s mission to help individuals and families better manage chronic illness and maintain healthy lives and with NCI?s commitment to research on survivorship, pediatric cancer, and cancer control.